1. Field of Invention
This invention relates to an injector for injecting adhesives of a type comprising a cylinder provided with a nozzle on a front end thereof and a piston which is movable forwardly in the cylinder by compressive means. Adhesive injectors of the type of this invention are particularly useful for repairing concrete constructions by injecting adhesives into cracks occurring in the concrete constructions by connecting the nozzles to injection pipes affixed at the cracks.
2. Description of Prior Art
Several dispensers or injectors of this kind are generally known to those skilled in the pertinent art, several having been disclosed in U.S. Pat. No. 4,861,401 and U.S. Pat. No. 3,905,521, for example.
The injector disclosed in U.S. Pat. No. 4,861,401 employs a method in which a piston is moved forwardly toward a front end by putting rubber belts between hook portions respectively provided on a rear end of the piston and a front end of a cylinder. Accordingly, it is necessary, when the injector is carried to a work location with the cylinder filled with adhesive, to apply the rubber belts for forward movement of the piston after the nozzle is connected to the injection pipe.
In this prior-art injecting method, however, there are several disadvantages to be overcome. The mentioned step of applying the rubber belt after connecting the nozzle to the injection pipe must be performed at a location of the injection work, during which the injector should be kept vertical. As a result, it sometimes happens that the injection pipe is broken due to an overload imposed trying to keep the injector vertical. Moreover, such a step as applying the rubber belt at the working location is not desirable from the viewpoint of working efficiency.
In the dispenser disclosed in U.S. Pat. No. 3,905,521 a coiled spring inserted in a cylinder is compressed to give impetus, or to drive, a piston during rearward movement thereof. A recess is provided in a main shaft of the piston, and movement of the piston is regulated by a pin, or sleeve, inserted in the cylinder at the recess, and retained at a rear edge portion of the cylinder, after filling the cylinder with adhesive.
In regulation of movement of the piston with such a sleeve inserted along the main shaft, there is a disadvantage of excessively large frictional resistance between the sleeve and the rear edge of the cylinder due to compressive force already given to the main shaft and concentrated thereon, eventually resulting in difficulty of drawing out the sleeve, or pin, when completing the connection of the nozzle to the injection pipe.